As a natural linear polysaccharide, alginate can be gelled into calcium alginate fiber and exploited for functional material applications. Owing to its high hygroscopicity, biocompatibility, nontoxicity and non-flammability, calcium alginate fiber has found a variety of potential applications. This article gives a comprehensive overview of research on calcium alginate fiber, starting from the fabrication technique of wet spinning and microfluidic spinning, followed by a detailed description of the moisture absorption ability, biocompatibility and intrinsic fire-resistant performance of calcium alginate fiber, and briefly introduces its corresponding applications in biomaterials, fire-retardant and other advanced materials that have been extensively studied over the past decade. This review assists in better design and preparation of the alginate bio-based fiber and puts forward new perspectives for further study on alginate fiber, which can benefit the future development of the booming eco-friendly marine biomass polysaccharide fiber.

A novel fiber dressing was fabricated by blending nano-silica or hydroxyapatite with alginate via microfluidic spinning, which demonstrated delayed degradation, greater mechanical performance and superior bioactivity due to the reinforcing alginate fibers. The prepared fibrous dressings exhibited higher surface area and porosity, which was conducive to cell growth. The addition of nano-silica and hydroxyapatite particles in the alginates improved the mechanical properties and biomineralization on the surface of the fibers. Besides, the degradation time scale and swelling behavior of the nanoparticle reinforced alginate fibers were delayed compared to the original alginate fibers, indicating a longer duration in contact with the wound. The prompt proliferation of fibroblast and keratinocyte cells suggested no significant cytotoxicity of the alginate containing silica and hydroxyapatite. Taken together, porous alginate fibers reinforced by nano-silica and/or hydroxyapatite showed high potential for wound dressing applications.

Alginate microfibres were fabricated by a simple microfluidic spinning device consisting of a coaxial flow. The inner profile and spinnability of polymer were analysed by rheology study, including the analysis of viscosity, storage modulus and loss modulus. The effect of spinning parameters on the morphological structure of fibres was studied by SEM, while the crystal structure and chemical group were characterized by FTIR and XRD, respectively. Furthermore, the width and depth of grooves on the fibres was investigated by AFM image analysis and the formation mechanism of grooves was finally analysed. It was illustrated that the fibre diameter increased with an increase in the core flow rate, whereas on the contrary of sheath flow rate. Fibre diameter exhibited an increasing tendency as the concentration of alginate solution increased, and the minimum spinning concentration of alginate solution was 1% with the finest diameter being around 25 µm. Importantly, the grooved structure was obtained by adjusting the concentration of solutions and flow rates, the depth of groove increased from 278.37 ± 2.23 µm to 727.52 ± 3.52 µm as the concentration varied from 1 to 2%. Alginate fibres, with topological structure, are candidates for wound dressing or the engineering tissue scaffolds.

Petroleum-based polymer fire-resistant fabric is not considered as eco-friendly, and has other problems like heavy weight and irritating tickling. On the other hand, even though Ca–alginate fiber is a natural fire-resistant polysaccharide derivative, its low tensile strength prevents the fiber from being a potential fire-resistant material. To enhance its mechanical performance, cellulose nanocrystal (CNC) functioned as reinforced nanofiller, assisted by a small amount of propanol to improve CNC dispersion in solution. CNC-doped alginate fiber (pC–Alg) was fabricated by the microfluidic spinning technique, and the effects of CNC content and the drawing ratio on the fibrous mechanical performance were investigated. Comparative studies indicated that a combination of 0.50 wt.% CNC, 6.00 v.% propanol, and 1.6 draft ratio helped pC–Alg fiber to achieve outstanding breaking strength of around 2.00 cN/dtex. It was shown that the use of propanol solvent and the incorporation of CNC can effectively eliminate CNC aggregation and reach a three-fold better tensile performance than the control. Limiting oxygen index test also showed that the resultant hybrid pC–Alg fiber still displayed good flame retardancy, making it an ideal candidate for fire-protection clothing.